Electrical cartridge-type heater

ABSTRACT

An electrical cartridge-type heater has a metal sheath containing a heating coil embedded in an insulating core. Connections between the coil and terminal pins are made by means of flat conductor strips which are wound around the pins and compressed by surrounding insulation. An improved method for securing the connector strips to the embedded portions of the terminal pins comprises twisting the strips about their longitudinal axes, inserting the twisted strips in preformed passages in the core member, pressing the terminal pins into the passages against the spiral surfaces of the twisted strips, to cause the strips to become entwined around the pins, installing the core assembly in a metal sheath, and then swaging the assembled unit.

United States Patent [1 1 Lindroth et al.

[ 1 Apr. 29, 1975 ELECTRICAL CARTRlDGE-TYPE HEATER [75] Inventors:Herbert L. Lindroth, Ballwin; Carl E. Barker, Overland, both of Mo.

[73] Assignee: Industrial Engineering and Equipment Co., St. Louis, Mo.

[22] Filed: May 28, 1974 [21] Appl. No.: 473,288

[52] vU.S. Cl. 338/302; 29/511; 29/619; 219/541; 338/240; 338/270;338/331 [51] Int. Cl 1101c 3/00 [58] Field of Search 338/238, 240, 302,331, 338/276, 270; 219/541; 29/511, 619

[56] References Cited UNITED STATES PATENTS 3,310,769 3/1967 Simmons338/270 3812580 5/1974 Drugmand 338/240 X Primar E.\'uminerE. A.Goldberg [5 7] ABSTRACT An electrical cartridge-type heater has a metalsheath containing a heating coil embedded in an insulating core.Connections between the coil and terminal pins are made by means of flatconductor strips which are wound around the pins and compressed bysurrounding insulation. An improved method for securing the connectorstrips to the embedded portions of the terminal pins comprises twistingthe strips about their longitudinal axes, inserting the twisted stripsin preformed passages in the core member, pressing the terminal pinsinto the passages against the spiral surfaces of the twisted strips, tocause the strips to become entwined around the pins, installing the coreassembly in a metal sheath, and then swaging the assembled unit.

10 Claims, 5 Drawing Figures 1 ELECTRICAL CARTRIDGE-TYPE HEATERBACKGROUND OF THE INVENTION The present invention relates to electricalcartridgetype heaters, and methods of manufacturing thesame. A failureof many cartridge heaters is the result of faulty connections betweenthe heater coil and the terminal pins. In heaters where there is nopositive coupling of these parts, as where the coil ends and pins areheld together merely by the surrounding insulating material, a highresistance junction and in some instances internal arcing may occur.

The conditions is particularly manifest in heaters wherein the coil endsextend along the terminal pins in the surrounding insulating core andwhich, at best make only linear contact with the pins. Contact andconductance may be further diminished by the entry of powderedinsulating core material between the confronting conductors. Such poorconnections often result in excessively high internal temperatures thatcause early failure of the heater.

The principal object of the present invention is to provide improvedmeans and a method for producing a positive surface-tosurface, lowresistance electrical connection between the heat coil and terminalpins, inside the ceramic core of the heater unit, and to accomplish thesame by a simple procedure and means that do not materially increasemanufacturing costs.

SUMMARY OF THE INVENTION In an electrical cartridge-type heater of thepresent invention connections between ends of the heater coil andterminal pins are made with the use of short strips of conductor ribbon.The connector strips are initially twisted, then inserted intorestricted passages in a ceramic core body upon which the heater coil iswound. Ends of the strips are secured to the coil ends outside the core,and terminal pins are then inserted into the passages against thetwisted surfaces of the strips to cause the strips to become tightlyentwined around the pins. Thereafter the core assembly is installed in atubular metal sheath and the unit is laterally compressed by swaging.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 of the drawings is a plan viewof a preformed connector strip;

FIG. 2 is a plan view, partly in section, illustrating the core assemblywith connector strips in place, prior to installation of terminal pins;

FIG. 3 is a longitudinal sectional view of the heater assembly with allparts in place but prior to a swaging and trimming operation;

FIG. 4 is a longitudinal sectional view through the unit followingswaging and trimming, and

FIG. 5 is a transverse sectional view taken at line 5-5 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT As appears in FIG. 4 thecartridge heater of the present invention comprises a tubular metalcasing 6 containing a cylindrical core member 7 formed of a compactedbody of refractory insulating material, such as magnesium oxide. Ahelical coil 8 of resistance wire, wound on core 7, is embedded in alayer 9 of refractory material that surrounds the core assembly andinsulates the coil from the casing. A pair of terminal pins 10 extendlongitudinally through core 7 and are connected each to one end of thecoil 8 by elements 11 formed of flat wire ribbon. These connectorelements are entwined around the pins and are held in intimate surfacecontact therewith within the compacted core 7. Pins 10 project outwardlyfrom one end of the unit, extending through a closure plug 12 at thatend, and at the opposite end of the unit the pins abut an insulatingdisc that separates the pins from a metal closure disc 14 which iswelded to the casing wall.

Curciform elements 15, FIG. 5, are formed of refractory material and areprimarily employed to support the core assembly centrally within thecasing during the assembly process, as will be explained.

As shown in FIG. 2 the preformed core member 7 is provided with a pairof parallel passages 15 for receiving the terminal pins, and also withlateral recesses 17 at opposite ends of the core, each recesscommunicating with one of the passages. Passages 16 are slightly largerin diameter than that of the terminal pins, but desirably such that thepassage diameter does not exceed the pin diameter by more than twice thethickness of the ribbon from which the connector elements 11 are made.The coil 8 is wound on the core so that a number of the end turns 8athereof extend across the passages 15 at the recesses 17.

The connector elements 11 are simply formed from short strips ofconductor ribbon by twisting the strips about their longitudinal axesone or more full turns, and bending an end portion of each twisted stripto form a crook 110, as shown in FIG. 1.

After the coil 8 has been wound on the core member 7 as above describedthe twisted elements 11 are inserted into the core passages 15, one fromone end of the core member and the other from the opposite end, and thetransversely bent end portions 11a of the elements are hooked over endturns of the coil and clamped thereto. With the twisted strips held inplace as described the terminal pins are slid into the passages againstthe spiral surfaces of the elements 18, the effect of which is to causethe elements to entwine around and come into surface contact, asdistinguished from linear contact, with the pins.

With the pins thusly in place in the core-coil assembly, projecting asubstantial distance from one end of the core and protruding slightlyfrom the opposite end, the cruciform spacer elements 15 are threaded onthe pins, one at each end, and the assembly is inserted into the casingcontaining the insulating disc 13 resting upon the inner surface of themetal closure disc 14. At this stage of the assembly process theelements 15 serve to support core assembly coaxially within the casing,with the coil 8 narrowly spaced therefrom.

The interior space surrounding the core assembly is then packed withpowdered magnesium oxide or the equivalent. Such material is introducedinto the open end of the casing, and, while the assembly is beingvibrated, caused to pass through the marginal openings in spacer discs15 to fill completely all voids in the casing. Thereafter, the lavaclosure plug 12, threaded on the terminal pins, is pressed into placeagainst spacer disc 15, and a temporary plug 20 (FIG.3), of plastic, isinstalled in similar manner within the open end of the casing andagainst the plug 12.

The assembled unit is subjected to lateral compaction, as by swaging,which has the effect of crushing the core member 7, pressing thematerial thereof tightly against the pins and connector strips 11 andbinding all parts together into a solid unit. Finally. the casing issevered in the plane of the outer face of the plug 12 and the excesscasing portion with temporary plug removed. In the same operation theextreme end of the tubular casing may be turned inwardly over the outeredge of plug 12 to secure and seal that member in place.

The herein-described method and construction has important advantagesover known constructions and methods, particularly with reference to thedescribed provisions for obtaining a superior internal connection.mechanically and electrically. between the resistor coil and theterminal pins.

We claim:

1. An electrical heating unit comprising:

a. a core of insulating material having a pair of passages extendingtherethrough,

b. a resistor coil wound on said core,

0. a pair of terminal pins in said passages. and

d. means interconnecting the ends of said resistor coil each to one ofsaid terminal pins, comprising strips of flat, longitudinally twistedmetallic ribbon extending longitudinally in said core passages andmaking surface to surface contact with said terminal pins.

2. The electrical heating unit described in claim 1 wherein:

e. said metallic ribbon connector strips extend spirally around saidpins and are held in intimate surface contact with said pins by saidinsulating material of the core.

3. The electrical heating unit of claim 2 wherein:

f. said strips have U-shaped end portions clamped to opposite endportions of the resistor coil.

4. An electrical cartridge heater including:

a. an insulating core having passages extending longitudinallytherethrough,

b. a resistor coil wound on said core,

0. terminal pins in said core passages, and

d. strip of flat wire connected to opposite ends of said coil, saidstrips extending individually into said passages and winding spirallyaround portions of the pins lodged in said passages.

e. said strips have bent end portions thereof clamped to opposite endportions of the resistor coil. 5 6. An electrical cartridge heater asset forth in claim 4, wherein:

f. said core is provided with lateral recesses at opposite ends thereof,each recess communicating with one of said passages, and

g. wherein said resistor coil has end turns traversing said recesses,and

h. said strips have reveresely bend end portions located within saidrecesses in clamping engagement with the portions of the resistor coilthat traverse said recesses.

7. The method of manufacturing electrical heaters which includes thesteps of:

a. winding a resistor coil on a preformed core member of insulatingmaterial having a pair of narrow passages extending therethrough,

b. inserting a strip of twisted metallic ribbon in each of saidpassages,

c. connecting end portions of said twisted strips to the end portions ofthe resistor coil, and

d. inserting terminal pins into said passages against the twistedsurfaces of said strips to cause said strips to entwine the pins.

8. The method described in claim 7 wherein:

e. said terminal pins are comprised of slender metallic rods of diameterto fit loosely within the core passages.

9. The method described in claim 8 wherein:

f. said terminal pins are inserted into the core passages from the sameends thereof in which said twisted metal strips are inserted.

10. The method defined in claim 7 wherein:

e. said core member is formed to provide lateral recesses eachcommunicating with one of the core passages, and i f. a connectionbetween the twisted strips and the resistor coil is made by clamping endportions of the strips to end turns of the resistor coil at said lateralCOI'C recess. 4 5

1. An electrical heating unit comprising: a. a core of insulatingmaterial having a pair of passages extending therethrough, b. a resistorcoil wound on said core, c. a pair of terminal pins in said passages,and d. means interconnecting the ends of said resistor coil each to oneof said terminal pins, comprising strips of flat, longitudinally twistedmetallic ribbon extending longitudinally in said core passages andmaking surface to surface contact with said terminal pins.
 2. Theelectrical heating unit described in claim 1 wherein: e. said metallicribbon connector strips extend spirally around said pins and are held inintimate surface contact with said pins by said insulating material ofthe core.
 3. The electrical heating unit of claim 2 wherein: f. saidstrips have U-shaped end portions clamped to opposite end portions ofthe resistor coil.
 4. An electrical cartridge heater including: a. aninsulating core having passages extending longitudinally therethrough,b. a resistor coil wound on said core, c. terminal pins in said corepassages, and d. strip of flat wire connected to opposite ends of saidcoil, said strips extending individually into said passages and windingspirally around portions of the pins lodged in said passages.
 5. Anelectrical cartridge heater as set forth in claim 4, wherein: e. saidstrips have bent end portions thereof clamped to opposite end portionsof the resistor coil.
 6. An electrical cartridge heater as set forth inclaim 4, wherein: f. said core is provided with lateral recesses atopposite ends thereof, each recess communicating with one of saidpassages, and g. wherein said resistor coil has end turns traversingsaid recesses, and h. said strips have reveresely bend end portionslocated within said recesses in clamping engagement with the portions ofthe resistor coil that traverse said recesses.
 7. The method ofmanufacturing electrical heaters which includes the steps of: a. windinga resistor coil on a preformed core member of insulating material havinga pair of narrow passages extending therethrough, b. inserting a stripof twisted metallic ribbon in each of said passages, c. connecting endportions of said twisted strips to the end portions of the resistorcoil, and d. inserting terminal pins into said passages against thetwisted surfaces of said strips to cause said strips to entwine thepins.
 8. The method described in claim 7 wherein: e. said terminal pinsare comprised of slender metallic rods of diameter to fit loosely withinthe core passages.
 9. The method described in claim 8 wherein: f. saidterminal pins are inserted into the core passages from the same endsthereof in which said twisted metal strips are inserted.
 10. The methoddefined in claim 7 wherein: e. said core member is formed to providelateral recesses each communicating with one of the core passages, andf. a connection between the twisted strips and the resistor coil is madeby clamping end portions of the strips to end turns of the resistor coilat said lateral core recess.